CN102879020A - Method for reducing non-linearity during measurement of a physical parameter and electronic circuit for implementing the same - Google Patents
Method for reducing non-linearity during measurement of a physical parameter and electronic circuit for implementing the same Download PDFInfo
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- CN102879020A CN102879020A CN2012102257389A CN201210225738A CN102879020A CN 102879020 A CN102879020 A CN 102879020A CN 2012102257389 A CN2012102257389 A CN 2012102257389A CN 201210225738 A CN201210225738 A CN 201210225738A CN 102879020 A CN102879020 A CN 102879020A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D3/00—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
- G01D3/028—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups mitigating undesired influences, e.g. temperature, pressure
- G01D3/032—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups mitigating undesired influences, e.g. temperature, pressure affecting incoming signal, e.g. by averaging; gating undesired signals
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
- G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
- G01D5/24—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance
- G01D5/241—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by relative movement of capacitor electrodes
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/14—Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators
- G01L1/142—Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators using capacitors
- G01L1/144—Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators using capacitors with associated circuitry
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P15/125—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by capacitive pick-up
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/18—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration in two or more dimensions
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Abstract
A method for reducing the non-linearity effect of a digital-analogue converter. An electronic circuit includes an amplifier and a digital-analogue converter for supplying a measuring voltage. The method includes biasing the capacitor electrodes by the measuring voltage on the basis of the first digital signal, then biasing the fixed electrode of the first capacitor at a regulated voltage and the fixed electrode of the second capacitor at a low voltage, then biasing the capacitor electrodes by the measuring voltage on the basis of a second digital measuring signal, and finally biasing the fixed electrode of the first capacitor at a low voltage and the fixed electrode of the second capacitor at a regulated voltage. A defined offset voltage is introduced into the digital-analogue converter to modulate the first and second digital signals. A mean is taken of the two digital signals to reduce the non-linearity effect of the converter.
Description
Technical field
The present invention relates to reduce the method for the nonlinear effect of the DAC converter in the control loop for during the physical parameters measurement by the capacitive sensor electronic interface circuit.Physical parameter can relate to acceleration, angular velocity, power or pressure.
The invention still further relates to the capacitive sensor electronic interface circuit for the method for the nonlinear effect that realizes reducing the DAC converter.Capacitive sensor consists of with the capacitor of two differential connections (differential connected) at least.Under the effect of for example power, the public electrode of capacitor can move between two fixed electordes, in order to change the capacitance of each capacitor.
Background technology
In simple traditional electrical capacitive sensor design, movably public electrode consists of the part that elasticity keeps (resiliently held) armature between two fixed electordes.In this case, capacitive sensor can be measured along a moving direction of traveling electrode.Under the effect of power, mobile certain distance of the direction of one or the other that traveling electrode can be in fixed electorde.
Use has such sensor of measuring axis, and public electrode is still in the distance about equally of two fixed electordes of distance, and it defines the capacitance that equates for two capacitors.Yet when public electrode moved under the effect of for example power, the capacitance of each capacitor changed on the contrary.The electronic interface circuit that is connected to capacitive sensor therefore so that analog output signal can be supplied to.This analog output signal adopts the form of the voltage of the capacitance variations that depends on two capacitors.
The such electronic interface circuit that is used for capacitive sensor is for example open at the article of Messrs H.Leuthold and F.Rudolph, and this article publication is at the A21-23(1990 of the periodical of " Sensors and actuators " by name) on the phase 278-281 page or leaf.
Capacitive sensor can be accelerometer, is used for carrying out acceleration analysis in conjunction with electronic interface circuit.It can be single-axis accelerometer, as above-mentioned capacitive sensor, or is multi-axial cord or three axis accelerometer meters, for the measurement of carrying out on three direction X, Y, the Z.Such three axis mems accelerometers can comprise a mass, namely are used for the public inertial mass of three pairs of differential capacitors, or are used for three right masses of capacitor.In the first situation, single public electrode and six fixed electordes are set, and in the second situation, setting has a public electrode of two fixed electordes to capacitor for each.
For the conditional electronic interface circuit that is used for such as the capacitive sensor of list or three axis mems accelerometers etc., output voltage is linear mode with the movement with respect to public traveling electrode ideally to be changed.Yet, because electronic circuit generally is integrated in the semiconductor substrate, the stray capacitance in the input must be taken into account, it is added to the electric capacity of sensor capacitor.In fact these stray capacitances do not rely on the movement of public electrode, and this has produced non-linear.Therefore, the electronic circuit output voltage does not change linearly with respect to the movement of public traveling electrode.These stray capacitances also have the susceptibility of reduction electronic circuit or the effect of gain.
MEMS sensor as accelerometer also is integrated in the semiconductor substrate, for example in the silicon substrate.This also brought with operating sensor during the relevant nonlinear problem of base material current potential.The base material current potential is difficult to control in the total of described sensor, because base material conducts electricity never fully.Under idle pulley, the traveling electrode of sensor also can be in the deviation post with respect to fixed electorde, and in the situation that does not have calibration, this can cause measuring error.Because these are non-linear, the electrostatic force that measures is non-vanishing under sensor and electronic circuit idle pulley.Owing to the impact of base material current potential on electrostatic force, the variation in this true power---it is applied on the public traveling electrode---that causes measuring, this is a shortcoming.
Usually, carry out power, acceleration or pressure survey in order to use electronic circuit, the fixed electorde of two capacitors or paired capacitor is periodically setovered with the voltage that has opposite polarity with respect to idle reference voltage or is encouraged.By with different voltage references two fixed electordes being setovered or polarized, striding the charge difference of traveling electrode can be measured and be converted at least one electronic circuit output voltage.When output voltage stabilization is on its end value, stride the total electrical charge vanishing of traveling electrode.These output voltages can be sampled and supply to treatment circuit, and this circuit can provide acceleration, power, pressure or the angular velocity data that depends on sensor construction.
Notice that tradition is used integrated electric capacitive sensor electronic interface circuit, the measurement of power, acceleration or pressure depends on the relevant offset voltage (offset voltage) of non-linear and any and unmatched electronic unit above-mentioned.Overcoming this solution of problem scheme proposes in EP patented claim No.1835263.
In EP patented claim No.1835263, by means of capacitive sensor, electronic circuit is carried out the measurement such as physical parameters such as acceleration, and capacitive sensor only comprises a pair of capacitor with the differential mode operation.Public electrode is connected to traditional electric charge and shifts amplifier, its output is connected to first integrator and second integral device, first integrator is supplied with the first analog output voltage in the measuring phases of First ray, the second integral device is supplied with the second analog output voltage in the measuring phases of the second continuous sequence.Therefore this electronic circuit is made of the disymmetry structure, and it has two integrators and two exciting units, is used for the fixed electorde with the form alternate run of integrated symmetric.
Therefore, in the phase one sequence, fixed electorde is setovered with the first output voltage, and setovers with height and the low-voltage-grade of voltage source.In the subordinate phase sequence, fixed electorde is setovered with the second output voltage, and setovers on the contrary with low and voltage levels and the phase one sequence of voltage source.Because this point is used two analogue integrator output voltages, changing the variation that causes by technology or supply voltage can minimize or eliminate.In addition, suppose electronic circuit with the identical double structure design of integrated symmetric operation, the base material current potential no longer exists or no longer has any large importance.
Yet a shortcoming of such electronic circuit of EP patented claim No.1835263 is that it provides the output signal of analog form, for example output voltage.This requires to use two integrators.Under these conditions, can not significantly reduce the size of integrating block and the power consumption of electronic circuit, if circuit tends to be integrated in the silicon substrate that uses the following CMOS technology of 0.18 μ m.In addition, electronic circuit only is arranged to a pair of capacitor that is connected to the capacitive sensor with single measurement axis.
WO patented claim No.2004/113930 discloses a kind of being connected to for the mono-axial of acceleration measurement or the electronic circuit of multi-axial cord capacitive sensor, and it can be quoted in this.Relevant with electronic circuit above-mentioned, after shifting amplifier, the electric charge that is connected to public traveling electrode is provided for the special logic that each measures axis, and it processes the digital measurement signal.One after the other for each axis, each logic is supplied with the binary measurement signal in output, and this characterization depends on traveling electrode with respect to the measuring voltage level of the movement of fixed electorde.The binary measurement signal one after the other supplies to digital analog converter in the control loop for each axis.With fixed electorde is biased to from stage of the high voltage of voltage source and low-voltage alternately, measuring in the stage of circulation for each of selected axis, this converter is fed to fixed electorde with measuring voltage.Use the digital signal processing in the amplifier output, the size reduction of electronic unit, the power consumption of electronic circuit output stage also reduces.Yet, the nonlinear measure that removes the non-linear and digital-analog convertor that can consist of owing to unmatched array of capacitors above-mentioned is not provided, this is a shortcoming.In addition, relatively long for each time of measuring the precise and stable digital output signal of axis, this is another shortcoming.
Also quotability of WO patented claim No.2008/107737, the method that it discloses a kind of electronic interface circuit for survey sensor and has been used for activating this electronic circuit.Survey sensor consists of with the capacitor of two differential connections, is used for acceleration measurement.After the capacitor fixed electorde had been biased, in the stage of measuring circulation, the analog input signal that is used for measuring was stored after electric charge shifts amplifier.So simulating signal is converted into the digital signal in the logic that is stored in electronic circuit.After this, digital signal is converted to simulation return signal with voltage form by digital analog converter, and it is applied to all the sensors electrode in each measures the successive stages of circulation.In measuring circulation, fixed electorde by the first biasing for the first time (a first time) be biased, and by being biased the second biasing second time (a second time) opposite with the first biasing.This so that leakage current can be removed from electronic circuit.Yet a large amount of steps of the method are essential for obtaining the physical parameters measurement signal in output, and this is a shortcoming.In addition, do not provide any non-linear any measure that compensates to the digital analog converter that may produce measuring error, this is a shortcoming.
Summary of the invention
Therefore, the object of the invention is to, by be provided at reduce rapidly and easily during the physical parameters measurement in the capacitive sensor electronic interface circuit non-linear---particularly in the digital-analog convertor in control loop---method, overcome the shortcoming of prior art above-mentioned.When electronic circuit was integrated, the size of parts also can reduce.
Therefore, the present invention relates to for the non-linear method that reduces for the digital analog converter of the capacitive sensor electronic interface circuit of measure physical parameters, it comprises the feature of mentioning in the claim 1.
The particular step of the method limits in dependent claims 2 to 6.
An advantage of this method is, makes the measurement of physical parameter with the first offset reference voltage, and the first offset reference voltage is different from zero and be added in the digital analog converter.On the one hand with the positive bias stage of fixed electorde, carry out in measuring circulation with the negative bias stage of fixed electorde on the other hand, the negative bias stage is opposite with positive bias such as the measurement of the physical parameter of acceleration etc.Depend on the first digital signal of positive integration and depend on the second digital signal of bearing integration and be stored in the logical block.So, obtain the average (mean) of two digital measuring-signals, be used for providing the digital output signal relevant with physical parameters measurement, it has the reduction of the nonlinear effect of digital analog converter.By first and second digital measurement signal is added together, remove any off-set value in output.In all continuous coverages circulation, and measure axis for each of sensor, each digital measurement signal is stored at least one particular register and upgrades.Point on each positive integration and the negative integral measurement curve also can be stored in the specific memory of logical block.
Advantageously, can get several physical parameters measurements for several different continuous offset voltages, and in succession be added to the operation transconductance amplifier (OTA) of digital analog converter.Be stored for each positive integration of each offset voltage and the point on the negative integral measurement curve.Two to five offset voltage value can be applied in, in order on all measured curves the output average is averaged, and provide the digital output signal of the large reduction with digital analog converter nonlinear effect.
Therefore, the invention still further relates to the electronic interface circuit for capacitive sensor, it is used for the method that realization reduces the nonlinear effect of digital analog converter, and this electronic interface circuit comprises the feature of mentioning in the claim 7.
The specific embodiment of this electronic circuit limits in dependent claims 8-10.
An advantage of physical sensors electronic interface circuit is that owing to the digital processing that is right after after electric charge shifts amplifier, it can provide rapidly the digital measurement signal of stabilization in output.These digital measurement signals are processed in logical block.Depending on the positive bias of fixed electorde of paired capacitor and two digital signals of negative bias is provided in logical block.Merge positive and negative digital signal and removed any variation that deliberately adds, thereby reduced the nonlinear effect of digital analog converter.Therefore, the non-linear of converter that causes owing to the not matching capacitor in the array of capacitors of digital analog converter partly is compensated by the measurement at least one non-vanishing bias voltage that adds.This has reduced the non-linear of electronic interface circuit, thus the more accurate acceleration analysis that realization is undertaken by electronic circuit.
Description of drawings
With reference to accompanying drawing, by following introduction, purpose, advantage and the feature that will more understand the method for the nonlinear effect that is used for reducing the digital analog converter on the capacitive sensor electronic interface circuit and be used for realizing the described electronic circuit of this method, in the accompanying drawings:
Fig. 1 shows in a simplified manner according to the present invention the capacitive sensor electronic interface circuit of the method for the nonlinear effect that realizes being used for reducing digital analog converter;
Fig. 2 shows the embodiment of a part of the digital analog converter of electronic circuit, and it has the electronic package be used to the nonlinear effect of the converter that reduces measure physical parameters; And
Fig. 3 shows for positive integration and the non-linear reduction curve that is used for the digital analog converter of the chart of transport function of the acceleration that measures of negative integration and the electronic circuit that the result obtains.
Embodiment
Because it is well-known in the art having the multiple parts of the sensor electronic interface circuit of differential capacitor, will no longer all explain in detail it in the following explanation.Emphasis mainly is placed on the method by the electronic circuit measure physical parameters, and this electronic circuit is supplied with digital measurement signal, the reduction with nonlinear effect of digital analog converter in output.
Fig. 1 shows the reduced graph of the multiple parts of the electronic interface circuit 1 that is used for capacitive sensor 2 according to the present invention.In this embodiment, three axis capacitive character MEMS sensors 2 with a mass are connected to electronic circuit 1, still, can expect connecting three axis sensors or mono-axial sensor with three moving mass pieces fully.Therefore this capacitive sensor is made of three couples of capacitor C1X, C2X, C1Y, C2Y, C1Z, C2Z.Two differential connections of capacitor that each is right.The public electrode CM of capacitor can be mobile between each is to two fixed electordes of capacitor under the effect of power, in order to consider the measurement of three axis X, Y, Z in pairs.As the function of the movement of public traveling electrode, electronic circuit 1 can be supplied with the digital measurement signal for each axis, and it is with relevant such as the physical parameter of acceleration, angular velocity, pressure or power etc.In the situation of acceleration analysis, electronic circuit can be configured to supply with the digital measurement signal between minimum and the maximum acceleration value.For example, can be chosen as electronic circuit arrangement as in the acceleration range of+2g, providing the digital measurement signal at-2g.For the acceleration of 1g, can count about change in voltage of 3 to 20mV.
Mobile electrode CM can consist of elasticity and remain on and be still in each to the part of the sensor armature in the centre position between two fixed electordes of capacitor C1X, C2X, C1Y, C2Y, C1Z, C2Z.Electronic circuit 1 can be by the power supply of continuous voltage source (not shown), its high voltage V after the first terminal is supplied with adjusting
REG, supply with low-voltage V at the second terminal
SSLow-voltage may be defined as 0V, and the high voltage after regulating can be set to for example 1.65V.In the operational mode of electronic circuit, the fixed electorde of each capacitor can be biased in high voltage V in the measurement cycle stage
REGOr low-voltage V
SSTherefore, when sensor 2 was static, because each two right capacitor C1X, C2X, C1Y, C2Y, C1Z, C2Z has equal capacitance, the voltage of striding public electrode CM was preferably the voltage V after equaling to regulate when static
REGWith the low-voltage V that is in 0V
SSBetween medium voltage V
REG/ 2.
The digital measurement signal that electronic circuit 1 is supplied with is proportional with two capacitor C1 and C2 with (C1-C2)/(C1+C2).In case the digital measurement signal is stabilization in the final physical parameter measurement, any flow of charge of striding each two right capacitor is cancelled.Therefore, the purpose of electronic circuit is, seeks the voltage that is applied to each fixed electorde at equalizing charge in the stage, and it satisfies (V
REG-V
DAC) C1=(V
DAC-V
SS) C2.This is working as V
DAC=(V
REG2) realize in the time of (1+(C1-C2)/(C1+C2)).
Comparer amplifier 4 has periodical IEEE J.Solid-State Circuits(1978 June, Vol.SC-13, pp294-297) in the disclosed type of article that is entitled as " A 1mV MOS comparer " very simply the design.This comparer amplifier 4 generally is included in the capacitor that is connected to public electrode CM in the input, thereafter for be used for output provide entirely have otherwise completely without the amplifier stage of digital signal.This electric charge shifts amplifier and has very high gain.When the voltage of striding traveling electrode CM increased through measuring the accumulating of positive charge in the circulation, amplifier output signal was in close to the voltage V after regulating
REGOne state.Yet when the voltage of striding traveling electrode CM reduced via measuring the accumulating of negative charge in the circulation, amplifier output signal became close to low-voltage V
SS" 0 " state.
The digital measurement signal of each register can be for example binary word of 10 bits.Counter is combined with processor, based on the signal that is provided by comparer amplifier 4, so that one state or " 0 " state will be placed on a binary word position.According to measuring method, before obtaining end value, two minutes (dichotomy) algorithms can be used for first and measure circulation.Therefore, highest significant position changes in each register, thereby begins to be stored in two minutes algorithms in the memory storage.Two stage by stage in, bit counter must change according to bit=comp XNOR pol, wherein, comp is the output valve of comparer amplifier 4, pol has defined positive bias or negative bias.The binary word of each register is adapted in each continuous measurement circulation and for each axis.
Each binary word DACbus of register measures in the circulation at each and in succession is fed to DAC digital analog converter 7, in order to binary word DACbus is converted to output voltage V
DACThis DAC output voltage allows all capacitor C1X, C2X, C1Y, C2Y, C1Z, C2Z and CM measuring the magnitude of voltage that discharges into the binary word DACbus that depends on particular axis in one of cycle stage.Binary word DACbus multiply by reference voltage V in the first multiplier of digital analog converter 7
DACin, reference voltage V
DACinFrom the pedestal generator with programmable-gain 6.This reference voltage can be by the voltage V that is connected to after the adjusting
REGWith ground V
SSBetween resistive voltage divider supply with.With reference to Fig. 2 explaination, provide two reference voltage V as following
DACin, be used for positive integration and negative integration.Be preferably, the first multiplier is defined as the OTA amplifier of explaining as following in Fig. 2, and it has and is provided as reducing the nonlinear modulation deviation voltage of converter.
Because binary word DACbus and OFFSETbus be on from 0 to 1023 10 bits, from the output voltage V of the negative bias (polarity " 1 ") of the positive bias (polarity " 0 ") of fixed electorde and fixed electorde
DACCan be expressed.Two voltage V
DACThese two formula eq(0) and eq(1) following expression:
eq(O)：V
DAC(O)=V
REG/2+V
DACoffset+(DACbus(0)-512)·K
DAC·V
REG+
(OFFSETbus-512)·K
OFF·V
REG
eq(1)：V
DAC(1)=V
REG/2+V
DACoffset-(DACbus(1)-512)·K
DAC·V
REG-
(OFFSETbus-512)·K
OFF·V
REG
K
DACBe a factor, it has defined system-gain.This gain can be by for example producing voltage V
DACinProgramme voltage V
DACinResitstance voltage divider from pedestal generator 6.K
OFFBe a factor, it has defined the gain of the regulating circuit of MEMS sensor voltage skew.This gain can adapt to according to the range of adjustment of hope, for example by producing voltage V
OFFin, voltage V
OFFinAnother resitstance voltage divider from pedestal generator 6.DACbus(0) defined 10 bit-binary words from the first register of logical block 5, it is applied to DAC converter 7 during the positive bias stage.From 0 to 1023 definition of this binary word.DACbus(1) defined 10 bit-binary words from the second register of logical block 5, it is applied to DAC converter 7 during the negative bias stage.From 0 to 1023 definition of this binary word.On the break-even point of rest position, 10 bits of encoded " 1000000000 " definition of the coding of each DACbus for value 512, it must define does not have the medium voltage of variation V
REG/ 2.OFFSETbus has defined 10 bit-binary and has regulated word, and it is applied to DAC converter 7, in order to the variation that is connected to the MEMS sensor is proofreaied and correct.V
DACoffsetThe noise voltage skew of the DAC converter 7 that expression hope removes.
Also will note, if just at acceleration measurement, DACbus(0) can be different from DACbus(1) because these binary words depend on the state of the biasing that is applied to fixed electorde.Yet OFFSETbus depends on the biasing that is applied to fixed electorde never in any form.Therefore, OFFESTbus selects after the preliminary step of proofreading and correct as mentioned above the MEMS sensor that is connected to electronic circuit forever.This scale-of-two is regulated word and can be stored in the memory storage of logical block 5.
In order to carry out for example measurement of the physical parameter of acceleration, measure circulation and generally consisted of by 12 successive stages.In 12 successive stages, there is a positive bias of the fixed electorde of three pairs of capacitors, and a negative bias of the fixed electorde of three pairs of capacitors.Between each biasing stage, according to each continuous binary word of the register of logical block 5, voltage V
DACBe applied on fixed electorde C1X, C2X, C1Y, C2Y, C1Z, the C2Z.The duration of stages can be the order of magnitude of 2 μ s.Be called in the stage of P0 all electrode for capacitors voltage V relevant with measuring one of axis
DACBiasing.Being called in the stage of P1, for the circulation of first semiperiod, positive bias is applied on the fixed electorde of the capacitor of measuring one of axis, and perhaps, the measurement circulation for second semiperiod applies negative bias.For each corresponding axis of measuring, there is the three phases P1 of every half period of measuring circulation.
By three axis sensors, several circulations in 12 stages repeat continuously, in order to obtain for example measurement of the physical parameter of acceleration.Measuring the once conversion of axis shifts corresponding to 16 electric charges.Three duration of measuring the conversion of axis can be less than 500 μ s, if stages has the following duration of about 2 μ s.Algorithm can be used in 8 initial measurement circulations in two minutes, and over-sampling can recycle for ensuing 8 samplings.
In order to understand the method for the nonlinear effect that reduces the digital analog converter on the electronic circuit, with reference to Fig. 2, it shows a part that has for reducing the converter of the nonlinear electronic package of the converter of measure physical parameters.According to the acceleration that will be measured by capacitive sensor, non-linear in the non-linear generation acceleration transport function (digital value) in the digital analog converter.The scale-of-two OFFSETbus that this part of the converter of Fig. 2 does not comprise the MEMS sensor regulates word and regulation voltage V from programmable-gain pedestal generator 6
OFFinMultiplier.
Will be noted that at first, the of paramount importance characteristic of this electronic circuit is that the digital value that represents each digital measurement signal of acceleration does not rely on any electronics skew.In fact, according to following formula, for the acceleration of 1g, each just and the digital value that provided by DACbus when finishing of negative stage for example+/-scope of 2g data in:
DAC_Ap=512 – offset+128 (forward counting device)
DAC_An=512+offset+128 (negative counter)
And
Digital_acceleration=DAC_Ap+DAC_An–1024
=(512–offset+128)+(512+offset+128)–1024=256
If the simulation of the electronic interface circuit of capacitive sensor part as an alternative+/-move in the scope of 4g, and if full scale be reduced to 2g by multiply by 2 numerical coding, the acceleration of 1g defines according to following formula:
DAC_Ap=512-offset+64 (forward counting device)
DAC_An=512+offset+64 (negative counter)
And
Digital_acceleration=2·(DAC_Ap+DAC_An–1024)=256
Will be noted that, the value of Digital-acceleration depends on the skew that exists or be added to electronic circuit never in any form, for the Digital-acceleration value that just is lower than 1g, the DACbus coding can be 512+63, if skew equals 0.
Above formula be to be correct under the condition of ideal linearity at the DAC converter only.If the DAC converter is made with the power capacitance technology, several non-linear mainly appearance when the most significant digit (MSB) of DACbus coding changes.
Therefore, digital analog converter comprises OTA17, is used on stages P0 is exporting measuring voltage V
DACBe fed to the electrode of capacitive sensor.Interrupteur SW D and integrating condenser Cfb parallel connection are connected to OTA output the negative input of the amplifier in the control loop.In the stage P1 that measures circulation, converter is in reseting stage, and amplifier OTA is in the follower pattern, and integrating condenser Cfb is by interrupteur SW
DShort circuit.In this stage P1, the electrode of a pair of MEMS sensor capacitor in the input is setovered with positive bias or negative bias.Each is in succession being biased among the stages P1 of capacitor in measuring circulation.Yet, in stage P0, be stored in that electric charge in the capacitor of capacitive character array is converted into signal com and to capacitor Cfb, therefore, output valve V
DACWhen finishing, stage P0 is ready to described voltage V
DACBe applied to all fixed electordes of MEMS sensor capacitor.
Digital analog converter also comprises the first array of capacitors 13 and the second migration array of capacitors 14, and it no longer is introduced.By charge transfer signal com is provided, all capacitor C1s, C1, C2 ..., C64, C128, C256 an electrode be connected to the negative input of OTA17.Another electrode of each capacitor of the first array 13 is via first-phase inductive switch SW
S_0, SW
1_0, SW
2_0, SW
6_0, SW
7_0, SW
8_0And second-phase inductive switch SW
S_1, SW
1_1, SW
2_1, SW
6_1, SW
7_1, SW
8_1Be connected to be used to the unit of selecting positive and negative integration 12.These switches all are used in the positive negative bias, but its switching sequence reverses according to the symbol of the binary word DACbus that is provided by logical circuit.
Therefore the first array of capacitors 13 is used in the control loop, and by the 10 bit-binary word DACbus control from logical block.This binary word DACbus is supplied with for each axis after positive bias and negative bias and one after the other by in 6 registers each.The capacitor of the first array has the value corresponding with 2 power.The size of each capacitor generally arranges based on particular comparator C1, and capacitance C2 equals 2C1, until the capacitance of C256 equals 256C1.Capacitor C1s has the capacitance corresponding with the capacitance of C1.This capacitor C1s and two interrupteur SW
S_0, SW
S_1Be used for " 1000000000 " DACbus coding (negative value), with respect to code " 1000000000 ", when code " 0111111111 " is effective, the skew of existence-1LSB, otherwise these two codings may not mate any electric charge to be shifted.Capacitor C1 generally can matched well to C256, and not strictly corresponding to the value about 2 true power of the capacitance of single capacitor C1.Therefore, according to the acceleration that the MEMS capacitive sensor in the input of electronic circuit interface is measured, this has produced non-linear in the control loop.For example, in fact large capacitor C64---its value should be 64C1---can have value C66 rather than C64, and this causes the error for the control loop of acceleration analysis, particularly from C63(C1+C2+C4+C8+C16+C32) during the transfer of C64.
Positive and negative integration selected cell 12 comprises for positively biased two interrupteur SW p and two interrupteur SW n being used for negative bias.Two reference voltage V from the first resitstance voltage divider DR111 that can be in pedestal generator
DACinpAnd V
DACinnBe supplied to selected cell 12.This first resitstance voltage divider DR111 is connected to V
REGAnd V
SSBetween.But when having negative integration, reference voltage V
DACinpBe supplied to the interrupteur SW of the first array of capacitors
S_0, SW
1_0, SW
2_0, SW
6_0, SW
7_0, SW
8_0, and reference voltage V
DACinnBe supplied to interrupteur SW
S_1, SW
1_1, SW
2_1, SW
6_1, SW
7_1, SW
8_1When having positive integration, reference voltage V
DACinnBe supplied to the interrupteur SW of the first array of capacitors
S_0, SW
1_0, SW
2_0, SW
6_0, SW
7_0, SW
8_0, and reference voltage V
DACinpBe supplied to interrupteur SW
S_1, SW
1_1, SW
2_1, SW
6_1, SW
7_1, SW
8_1Therefore, be applied to the voltage V of switch
DACinnAnd V
DACinpBetween positive and negative integration, reverse.This allows the transfer charge sign-inverted of transducer signal " com ".
In order to reduce the nonlinear effect of the digital analog converter on the electronic circuit, the offset voltage dvref of regulation also is added to the reference voltage V of the voltage signal Vref of the positive input that is fed to OTA
REG/2Must also the OTA skew be taken into account, it also is added to this reference voltage signal, and owing to the non-match error of the element that is connected to OTA consists of the noise voltage source.Be added to voltage V
REG/ 2 regulation offset voltage dvref supplies with via the second resitstance voltage divider 6 of the array that is connected to switch 15, and the array of switch 15 is controlled by 4 bits match word T_vref.These switch arrays can be the multiplexer of the resistor that is connected to the second resitstance voltage divider, and by coupling word T_vref control.Each bit of this coupling word can be supplied with the voltage difference of the order of magnitude of 3.3mV.V
REGSelectable voltage range around/2 can be from-26.4mV to+23.1mV.
Shown in Figure 3 such as following reference, in order to reduce the nonlinear effect of the digital analog converter on the electronic circuit, generally to the voltage V of the reference voltage V ref of the positive input that is fed to OTA17
REG/ 2 add or are enough from it non-zero offset voltage dvref that deducts regulation.Usually, the offset voltage dvref of this regulation must be greater than or less than OTA_offset voltage, is different from V in order to have in the positive OTA input
REG/ 2 reference voltage (skew) value is for the positive integrated curve of the digital value that realizes this point, get having self-corresponding logical block register and the average of negative integrated curve.Therefore, since the error that the unsuitable coupling of one or the other capacitor of the first array of capacitors causes reduce by half.Be preferably, several measurements are carried out at different offset voltage dvref, in order to define for example several curves, for example measure curves for five.These five averages of measuring curve are so that the nonlinear effect of the digital analog converter on the electronic circuit even further reduction.Because positive bias and negative bias are added to voltage V
REG/ 2 or from voltage V
REG/ 2 any offset d vref that deduct remove from the logical block digital output signal certainly, and only accekeration is determined in these digital signals.
For positive integration, at the voltage V of digital analog converter output supply
DACDetermined by following formula:
V
DAC=V
Ref+ OTA_offset+ (V
DAC_inp-V
DAC_inn) (C1/Cfb) (DACbus-512) V
DAC=V
REG/ 2+dvref+OTA_offset+ (V
DAC_inp-V
DAC_inn) (C1/Cfb) (DACbus-512) wherein, DACbus is 10 bit digital values, dvref will be for being added to V among the reference voltage signal Vref
REG/ 2 voltage difference.
The logical block that is connected to converter changes DACbus, until realize charge balance at the MEMS sensor, and this point occured in the following moment:
V
DAC=V
REG/2·(1+(C1-C2)/(C1+C2))
Therefore,
dvref+OTA_offset+(V
DAC_inp-V
DAC_inn)·(C1/Cfb)·(DACbus-512)=(V
REG/2)·(C1-C2)/(C1+C2))
This causes:
DACbus=512+(Cfb/C1)·((V
REG/2)·(C1-C2)/(C1+C2)-(dvref+
OTA_offset))/(V
DAC_inp-V
DAC_inn)
DACbus=512-(Cfb/C1)·(dvref+OTA_offset)/(V
DAC_inp-V
DAC_inn)+
(Cfb/C1)·((V
REG/2)·(C1-C2)/(C1+C2))/(V
DAC_inp-V
DAC_inn)
For negative integration, the voltage VDAC that supplies with in digital analog converter output is determined by following formula:
V
DAC=V
REG/2+dvref+OTA_offset-(V
DAC_inp-V
DAC_inn)·(C1/Cfb)·(DACbus-512)
And
V
DAC=(V
REG/2)·(1-(C1-C2)/(C1+C2))
Therefore:
dvref+OTA_offset-(V
DAC_inp-V
DAC_inn)·(C1/Cfb)·(DACbus-512)
=-(V
REG/2)·(C1-C2)/(C1+C2))
This causes:
DACbus=512+(Cfb/C1)·((V
REG/2)·(C1-C2)/(C1+C2)+(dvref+
OTA_offset))/(V
DAC_inp-V
DAC_inn)
DACbus=512+(Cfb/C1)·(dvref+OTA_offset)/(V
DAC_inp-V
DAC_inn)+
(Cfb/C1)·((V
REG/2)·(C1-C2)/(C1+C2))/(V
DAC_inp-V
DAC_inn)
Value (dvref+OTA_offset) is offset corresponding to electronic circuit.This value item (Cfb/C1) (dvref+OTA_offset)/(V
DAC_inp-V
DAC_inn) the middle existence, have the opposite symbol for positive and negative integration.This produces for the error in the end value of the DACbus coding of positive and negative integration.Notice that the error of voltage Vref is equivalent to the OTA skew.Therefore, regulate the value of word T_vref by changing 4 bits, can modulation deviation voltage, in order to change the reference voltage V ref of the positive input that is fed to OTA.By changing offset voltage dvref, can change DACbus coding (DAC_Ap and DAC_An), and not change final accekeration, its digital value for producing by adding DAC_Ap and DAC_An.This offset voltage dvref can be used as the result who regulates word T_vref and changes several times in measuring circulation.This allows several curves to be determined and then quilt is average, thereby reduces any nonlinear effect of electronic circuit as far as possible.
Fig. 3 shows the curve acf of the average of the second curve ac2 of the first curve ac1 of positive integration, negative integration and two other curve, and its converter that is used for reducing during the acceleration analysis is non-linear.Defined offset voltage dvref selects with the value of the 0.2mV among Fig. 3.The first curve is from the ideal curve I1 deviation maximum error e1 of the acceleration analysis of the 1g order of magnitude.The second curve is from the ideal curve I2 deviation maximum error e2 of 1g acceleration analysis.Than maximum error e1 and the e2 of two other curve, the maximum error ef of the Mean curve of two other curve relevant with ideal curve If only is half.Certainly, if get the average of several positive and negative integrated curves, it is minimum that the maximum final error of Mean curve becomes, and Mean curve becomes close to ideal curve.Therefore, this any of capacitor who has effectively overcome the first array of capacitors of digital analog converter is not mated, and this is purpose of the present invention.
By the introduction that has provided, in the situation that does not break away from the scope of the present invention that claim limits, the multiple modification of electronic interface circuit that those skilled in the art can expect reducing for the method for the nonlinear effect of the digital analog converter on the electronic circuit of measure physical parameters and be used for realizing the capacitive sensor of the method.Can expect, relative to each other change the duration of stages, or in duration of each circulation of the operation of determining a plurality of curves that will be average or physical parameters measurement operation.The order of positive negative bias can be measured in the circulation at each and change.At least two additional phase of electronic circuit operation test also can be placed on each and measure in the circulation.
Claims (10)
1. be used for reducing the method for the nonlinear effect of the digital analog converter on the electronic interface circuit (1) of capacitive sensor (2) of measure physical parameters, described capacitive sensor (2) comprises the capacitor (C1X of at least two differential connections, C2X), its public electrode (CM) can physical parameter just when measured each fixed electorde with respect to two capacitors move, in order to change the capacitance of each capacitor, described electronic circuit comprises: electric charge shifts amplifier (4), and it is connected to public electrode (CM) via switch unit (3); Logical block (5), it is connected to amplifier output, is used for the data of being supplied with by amplifier are carried out digital processing, and is used for supplying with the digital measurement signal; Digital analog converter (7), it can be via switch unit (3) with measuring voltage (V
DAC) being fed to electrode, measuring voltage defines based at least one binary word (DACbus) conversion in the definition digital measurement signal, and the method is included in the following steps in each measurement circulation in succession:
A) via switch unit (3), based on from the first digital measurement signal of last circulation or the first initial binary word of being supplied with by logical block (5), use the measuring voltage (V that is supplied with by digital analog converter (7)
DAC), the electrode of capacitor (C1X, C2X, CM) to be setovered, the first digital signal depends on the first biasing of the fixed electorde of capacitor,
B) with from the high voltage (V after the adjusting of the voltage source of electronic circuit
REG) fixed electorde of the first capacitor (C1X) is setovered, with the low-voltage (V from voltage source
SS) fixed electorde of the second capacitor (C2X) is setovered, in order to the first digital measurement signal in the logical block (5) is adapted to,
C) via switch unit (3), based on from the second digital measurement signal of last circulation or by the second initial binary word that logical block (5) provides, use the measuring voltage (V that is supplied with by digital analog converter (7)
DAC), the electrode of capacitor (C1X, C2X, CM) is setovered, the second digital signal depends on the second biasing, second be biased to capacitor fixed electorde the first biasing oppositely, and
D) with the low-voltage (V from the electronic circuit voltage source
SS) fixed electorde of the first capacitor (C1X) is setovered, with from the high voltage (V after the adjusting of voltage source
REG) fixed electorde of the second capacitor (C2X) is setovered, in order to the second digital measurement signal in the logical block (5) is adapted to,
It is characterized in that, at the beginning, or in the physical parameters measurement circulation, the offset voltage (Vref) of regulation is introduced digital analog converter, in order to revise or modulate first and second digital signal, and it is characterized in that the average of first and second digital signal is obtained, in order to the digital output signal (OUT relevant with physical parameters measurement is provided
DX), wherein have the nonlinear effect of the digital analog converter that reduces.
2. according to claim 1 measuring method, it is characterized in that, the offset voltage of the several regulations that differ from one another (Vref) is introduced in the measurement circulation in succession of digital analog converter, and it is characterized in that, get the average of multiple the first digital signal and multiple the second digital signal, in order to supply with the digital output signal (OUT relevant with physical parameters measurement
DX), it has the nonlinear effect of the digital analog converter that reduces.
3. according to claim 2 measuring method is characterized in that, based on one in the offset voltage (Vref) of the regulation of in succession introducing digital analog converter, each first digital signal and each second digital signal are stored in the logical block (5).
4. according to claim 1 measuring method, wherein, digital analog converter (7) comprises: array of capacitors (13), it is one after the other controlled by the binary word of the first register and by the binary word of the second register; OTA amplifier (17), it is connected to an electrode of all capacitors of array of capacitors in negative input; Switch (SW
D) and integrating condenser (Cfb), it is connected to an output of OTA amplifier the negative input of the amplifier in the control loop in parallel, the positive input of OTA amplifier receives the offset voltage of regulation, measures the measuring voltage (V that supplies with in the output of OTA amplifier in the circulation in order to revise
DAC), the method is characterized in that logical block (5) comprises: the first register is used for storing positive integration the one 10 digital bit measuring-signal afterwards; The second register is used for the 2 10 digital bit measuring-signal after integration is born in storage; Storer is used for the physical parameters measurement result that circulation is measured in storage.
5. according to claim 1 measuring method, wherein, capacitive sensor is three axis types, it has the capacitor (C1X of three pairs of differential connections, C2X, C1Y, C2Y, C1Z, C2Z), all to or every pair have a public electrode (CM), every pair has two fixed electordes, and wherein, the logical block of electronic circuit (5) can be supplied with for each and measure axis X, Y, first and second digital measurement signal of Z is characterized in that, the method that is used for measure physical parameters comprises 12 stages in succession that each measures circulation, it comprises for each axis X, Y, Z in corresponding to the situation of the first digital signal of selected axis in the one or six stage one after the other repeating step a) and b), and for each axis X, Y, Z in corresponding to the situation of the second digital signal of selected axis in six last stages repeating step c one after the other) and d).
6. according to claim 1 measuring method, wherein, capacitive sensor is three axis types, it has the capacitor (C1X of three pairs of differential connections, C2X, C1Y, C2Y, C1Z, C2Z), all to or every pair have a public electrode (CM), every pair has two fixed electordes, and wherein, the logical block (5) of electronic circuit (1) can be supplied with for each and measure axis X, Y, first and second digital measurement signal of Z, it is characterized in that, the method that is used for measure physical parameters comprises 12 stages in succession that each measures circulation, and it is included in the situation of first and second digital measurement signal of X-axis line for X-axis line execution in step a) to d), the X-axis line after, a) arrive d for Y-axis line execution in step in the situation of first and second digital measurement signal of Y-axis line), finally, after the Y-axis line for z axis in the situation of first and second digital measurement signal of z axis execution in step a) to d).
7. the electronic interface circuit (1) that is used for capacitive sensor, it comprises the capacitor (C1X that pair of differential connects, C2X), be used for realization method according to claim 1, electronic circuit comprises: the electric charge that is connected to public electrode (CM) via switch unit (3) shifts amplifier (4); Be connected to the logical block (5) of amplifier output, be used for the data of being supplied with by amplifier are carried out digital processing, and for the first biasing of the fixed electorde that depends on respectively capacitor with as the first second reverse biasing of setovering, supply with first and second digital measurement signal; Digital analog converter (7), it can be via switch unit (3) with measuring voltage (V
DAC) be fed to electrode, measuring voltage defines based on binary word (DACbus) conversion relevant with the first digital measurement signal or the second digital measurement signal, it is characterized in that, the digital analog converter of electronic circuit (7) comprises electronic package (15,16), it can introduce converter with the offset voltage (Vref) of regulation, so as to revise or modulation logic unit (5) in first and second digital signal, thereby reduce nonlinear effect for the converter of physical parameters measurement.
8. according to claim 7 electronic circuit (1), it is characterized in that, digital analog converter comprises: array of capacitors (13), its binary word by the first register (DACbus) and one after the other controlled by the binary word (DACbus) of the second register; OTA amplifier (17), it is connected to an electrode of all capacitors of array of capacitors in negative input; Switch (SW
D) and integrating condenser (Cfb), it is connected to an output of OTA amplifier the negative input of the amplifier in the control loop in parallel, the positive input of OTA amplifier receives by electronic package (16, the offset voltage of the regulation of 15) supplying with is measured the measuring voltage (V that supplies with in the output of OTA amplifier in the circulation in order to be modified in
DAC).
9. according to claim 8 electronic circuit (1), it is characterized in that electronic package comprises: resistive voltage divider (DR2), it is connected to the low-voltage (V from voltage source
SS) and high voltage (V
REG) between; Switch arrays (15), it adopts the form of simulation multiplexer, is connected to the different nodes of resistive voltage divider in input, and regulates the offset voltage (Vref) that regulation supplied with in word (T_vref) based on scale-of-two in output.
10. according to claim 7 electronic circuit (1) is characterized in that comprising the pedestal generator (6) with programmable-gain, is used for the reference voltage (V that is programmed
DACinp, V
DACinn) be fed to the switch of array of capacitors (13) via plus or minus integration selected cell (12).
Applications Claiming Priority (2)
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|---|---|---|---|
| EP11172424.1A EP2541213B1 (en) | 2011-07-01 | 2011-07-01 | Method for reducing non-linearity during the measurement of a physical parameter and electronic circuit for implementing the same |
| EP11172424.1 | 2011-07-01 |
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Country Status (4)
| Country | Link |
|---|---|
| US (1) | US9097556B2 (en) |
| EP (1) | EP2541213B1 (en) |
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| CN106725834A (en) * | 2016-12-30 | 2017-05-31 | 重庆西山科技股份有限公司 | Automatic identification radio frequency handle and radio frequency operation component |
| CN110244882A (en) * | 2018-03-09 | 2019-09-17 | 辛纳普蒂克斯公司 | Mitigate the electromagnetic radiation from sensor electrode |
| CN111052059A (en) * | 2017-09-07 | 2020-04-21 | 赛普拉斯半导体公司 | Nano-power capacitance-to-digital converter |
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| EP2966454B1 (en) * | 2014-07-07 | 2017-08-30 | EM Microelectronic-Marin SA | Method for measuring a physical parameter, and electronic circuit for implementing same |
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Also Published As
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|---|---|
| EP2541213B1 (en) | 2017-03-08 |
| US20130006559A1 (en) | 2013-01-03 |
| TWI585368B (en) | 2017-06-01 |
| TW201315969A (en) | 2013-04-16 |
| EP2541213A1 (en) | 2013-01-02 |
| CN102879020B (en) | 2015-07-01 |
| US9097556B2 (en) | 2015-08-04 |
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